Short of copy pasting your scale animation on each one, I bet you could write a script for it. Unfortunately, I am terrible at it. Have you tried asking in Creative Cow's AE Expressions forum? Dan Ebberts hovers around there and he's pretty boss at this sort of thing.

If I'm understanding you correctly, you could just make an expression on the scale property like "transform.scale+10*index." Then Edit > Copy Expression Only, and paste it to all the other layers (the 10 is whatever amount you want to incrementally scale each layer by). Better yet, create a null in your comp with a slider control on it and pickwhip the value of it to replace the 10. That way you can change it on the fly. Scripts work too

If I'm understanding you correctly, you could just make an expression on the scale property like "transform.scale+10*index." Then Edit > Copy Expression Only, and paste it to all the other layers (the 10 is whatever amount you want to incrementally scale each layer by). Better yet, create a null in your comp with a slider control on it and pickwhip the value of it to replace the 10. That way you can change it on the fly. Scripts work too

A late thanks for this - appreciate the reply... ( but didn't get email notified about the reply )...

Turned out there was a simple solution.. just took me sleeping and waking up the next day to realise how easy it should've been - import 500 images into AE, and *before* sequencing them... ie while they're all in exact alignment under each other, just select all layers, and modify the scale values of the in and out points.... *then* sequence the layers.... and presto - each image is being slowly zoomed in on....

I can see how your method would be useful for increasing scale relative to the layer above it though... thanks!